This invention relates to a transparency and to a method of making the transparency, particularly, a transparency for the formation of an adherent electrostatic image thereon. More particularly, the invention relates to a clear film projection transparency used in a xerographic or electrostatographic reproduction process for formation thereon of an image especially suited for projecting onto a screen or other surface for viewing purposes.
Clear film projection transparencies in current use include two popular types: xerographic or plain paper copier transparencies, and thermal (infrared) transparencies. The xerographic transparencies are loaded into a plain paper copier (dry paper copier) in the same manner as plain paper used for making copies of an original. The xerographic transparencies accept a xerographic image of the original in the same manner as does paper. As is well known in the art, the image is formed by transferring a toner to a surface of the transparency, and the toner is fused into the surface, to provide a permanent copy. The thermal transparencies are imaged by exposure to infrared radiation in the presence of an original, with the image being formed chemically. Xerographic transparencies typically are made from a thin film of an organic resin, such as a polyester resin film, constituting a base sheet, and a resin coating or film on a surface of the base sheet which is compatible with the xerographic toner and the base sheet, and serves to anchor the xerographic image and minimize static electricity. The patent literature discloses that the resins employed in coatings on the base sheet include vinyl, acrylic, styrene, and linear polyester resins, and hydrophilic colloids of hydrolyzed cellulose acetate and hydroxethyl cellulose, as disclosed, for example, in U.S. Pat. Nos. 3,854,942; 3,949,148; 4,085,245; 4,259,422; and 4,320,186. The patents also disclose various problems encountered in the manufacture of such transparencies, including the problems of achieving good adherence of the image-forming toner to the transparency, avoiding image distortion, and reducing static electricity, so as to permit automatically feeding a plurality of stacked transparency sheets to the copier without interference caused by electrostatic attraction of adjacent sheets to each other. The ideal xerographic transparency should be nearly static-free, highly transparent, and have a scratch-resistant coating, and when xerographically imaged, should have a well-adhered, faithful image, not subject to cracking, and having a high contrast ratio. In providing such a transparency, various other problems are to be avoided or minimized, including curling, sticking, fogginess, splotches, streakiness, waviness, rainbowing, and wrinkling.